The present invention relates generally to a magnetic tape cassette with a tape protective closure for openably closing an opening of a cassette casing. More specifically, the invention relates to a magnetic tape cassette, such as a pulse-code modulated (PCM) audio cassette, which has a tape protective closure and means for normally biasing the closure to a closed position.
U.S. Pat. No. 4,572,461, issued to Horikawa et al. on Feb. 25, 1986, and assigned to the assignee of the present invention discloses a cassette casing for a magnetic tape cassette with an openable and closable pivotal closure lid at its front portion and an openable and closable sliding shutter member at its lower surface. While the magnetic tape is not in use, the sliding shutter member covers the underside of the magnetic tape cassette to cover the reel shaft insertion apertures, and a cut-out for receiving a tape loading mechanism of a recording and/or reproducing apparatus. The pivotal closure lid and sliding shutter member couple while in the closed position. The sliding shutter member is biased toward the closed position by means of a coil spring.
A drawback is encountered in this mechanism due to the presence of the coil spring biasing the sliding shutter member toward the closed position. Specifically, in order to accommodate the coil spring, some clearance must be provided between the lower surface of the cassette casing and the upper surface of the sliding shutter member. This limits how thin the magnetic tape cassette can be made.
In addition, in order to anchor the front end of the coil spring, a spring anchor column must be formed in the lower section of the cassette casing, and in order to anchor the rear end, a spring anchor member must be formed in the sliding shutter member. The front and rear ends of the coil spring most also be hooked onto the spring anchor column and the spring anchor member during assembly. This makes assembly rather troublesome and thus degrades the manufacturing productivity of the magnetic tape cassette.